Denominator while calculating secondary attack rate following a person with a primary disease is: March 2009

Ans. A: All the contacts who are exposed to the affected A secondary attack rate measures the frequency of new cases of a disease among the contacts of known cases. This can be very impoant for diseases that are spread from person to person, such as tuberculosis, measles, shigellosis, and varicella. Secondary attack rates are often calculated for households. To calculate the number of household contacts (denominator), subtract the number of primary cases from the total number living in the households. In some situations, contacts in other settings may be investigated (for example, residents of a homeless shelter, or people who work in a specific building). The calculation is done in the same way as for household contacts.